Behavioral and Brain Sciences



Why people see things that are not there: A novel Perception and Attention Deficit model for recurrent complex visual hallucinations


Daniel Collerton a1, Elaine Perry a2 and Ian McKeith a3
a1 South of Tyne and Wearside Mental Health NHS Trust, Bensham Hospital, Gateshead NE8 4YL, United Kingdom daniel.collerton@ncl.ac.uk
a2 MRC Building, Newcastle General Hospital, Newcastle-upon-Tyne NE4 6BE, United Kingdom e.k.perry@ncl.ac.uk
a3 Wolfson Research Unit, Institute for Aging and Health, Newcastle General Hospital, Newcastle-upon-Tyne NE4 6BE, United Kingdom i.g.mckeith@ncl.ac.uk

Abstract

As many as two million people in the United Kingdom repeatedly see people, animals, and objects that have no objective reality. Hallucinations on the border of sleep, dementing illnesses, delirium, eye disease, and schizophrenia account for 90% of these. The remainder have rarer disorders. We review existing models of recurrent complex visual hallucinations (RCVH) in the awake person, including cortical irritation, cortical hyperexcitability and cortical release, top-down activation, misperception, dream intrusion, and interactive models. We provide evidence that these can neither fully account for the phenomenology of RCVH, nor for variations in the frequency of RCVH in different disorders. We propose a novel Perception and Attention Deficit (PAD) model for RCVH. A combination of impaired attentional binding and poor sensory activation of a correct proto-object, in conjunction with a relatively intact scene representation, bias perception to allow the intrusion of a hallucinatory proto-object into a scene perception. Incorporation of this image into a context-specific hallucinatory scene representation accounts for repetitive hallucinations. We suggest that these impairments are underpinned by disturbances in a lateral frontal cortex–ventral visual stream system. We show how the frequency of RCVH in different diseases is related to the coexistence of attentional and visual perceptual impairments; how attentional and perceptual processes can account for their phenomenology; and that diseases and other states with high rates of RCVH have cholinergic dysfunction in both frontal cortex and the ventral visual stream. Several tests of the model are indicated, together with a number of treatment options that it generates.



Key Words: Blindness; Charles Bonnet; cholinergic; cortical release; delirium; dementia; dream intrusion; hallucination; Perception and Attention Deficit (PAD) model; schizophrenia.


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